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Often the easiest thing is to pop to PC World, then at least if it doesn't work you can take it back and shout at someone.
Unfortunately they're all deaf in PC World! Shouting will get you nowhere. They are just not interested.
It's a fact, I've sued PCWorld more times than any other supplier. My understanding is that DSG have a bigger litigation dept. than they do customer services dept. That just about sums it up.
You can generally get far more for your £s elsewhere.
Another vote for Novatech...been using them for probably 15+ years. But then again, I'm comfortable building from the ground up. Their barebones systems are ideal if you're upgrading an existing setup - latest is i5 6600K Skylake, 16Gb RAM, 500Gb SSD, 2Tb HDD. Graphics are nothing fancy - 4Gb GeForce GT630 driving a WQHD 2560 x 1440 27" monitor + 40" TV (via HDMI) for BKOOL.
However, BKOOL really doesn't need a beefy PC. A much lower specced PC will do the job just fine, as it does when I use the laptop, if I connect downstairs in front of the 50" TV - when the wife & family are away without me!